The present invention relates to a variable valve operating system of an engine enabling working angle and phase to be varied, and specifically to a variable valve operating system of an internal combustion engine employing a variable working angle control mechanism and a variable phase control mechanism both used for an intake valve.
In recent years, there have been proposed and developed various variable valve operating systems enabling both working angle and phase to be varied for a high degree of freedom of valve lift characteristics and enhanced engine performance through all engine operating conditions. Such variable valve operating systems have been disclosed in Japanese Patent Provisional Publication Nos. 2001-280167 (hereinafter is referred to as xe2x80x9cJP2001-280167xe2x80x9d) and 2002-89303 (hereinafter is referred to as xe2x80x9cJP2002-89303xe2x80x9d). In the system disclosed in each of JP2001-280167 and JP2002-89303, a hydraulically-operated variable working angle control mechanism is provided to continuously extract or contract a working angle of an intake valve, and a hydraulically-operated variable phase control mechanism is provided to retard or advance the angular phase at the maximum intake-valve lift point (often called xe2x80x9ccentral-angle phasexe2x80x9d). In particular, in the system of JP2001-280167, to avoid a rapid drop in hydraulic pressure, that is, an excessive load on an oil pump serving as a hydraulic pressure source common to both the variable working angle control mechanism and the variable phase control mechanism, a control system inhibits the two control mechanisms from being driven simultaneously in specified transient states, such as in presence of a transition from low to high load or in presence of a transition from high to low load. In other words, in the system of JP2001-280167, when the working angle and the central-angle phase have both to be varied greatly during the transient state, the control system first drives one of the two control mechanisms and then drives the other with a time delay.
In such a variable valve operating system employing both a first actuator for a variable working angle control mechanism and a second actuator for a variable phase control mechanism, a certain valve lift characteristic is realized or achieved by way of a combination of a change in working angle adjusted by the first actuator and a change in central-angle phase adjusted by the second actuator. The inventors have discovered that, in the transient state, i.e., in presence of a remarkable engine load change, a variation of working angle (in particular, a time rate of change of working angle adjusted by the first actuator) is not always identical to a variation of central-angle phase (in particular, a time rate of change of central-angle phase adjusted by the second actuator), and therefore there is an increased tendency for a transient valve lift characteristic to deviate from a desired valve lift characteristic. Such a deviation leads to excessive valve overlap, reduced combustion stability, increased combustion deposits or undesired torque fluctuations. Thus, it is desirable to more precisely optimize a valve lift characteristic, which is determined by the working angle and central-angle phase, in transient states, for example, in presence of a transition from low to high load or a transition from high to low load.
Accordingly, it is an object of the invention to provide a variable valve operating system of an engine employing a variable working angle control mechanism and a variable phase control mechanism both used for an intake valve, capable of optimizing a valve lift characteristic, which is determined by the working angle and central-angle phase, in transient states, for example, in presence of a remarkable change in engine load.
In order to accomplish the aforementioned and other objects of the present invention, a variable intake-valve operating system for an engine enabling a working angle of an intake valve and a phase at a maximum lift point of the intake valve to be varied, comprises a variable working-angle control mechanism capable of continuously changing the working angle of the intake valve, a variable phase control mechanism capable of continuously changing the phase of the intake valve, a control unit being configured to be electronically connected to both the variable working-angle control mechanism and the variable phase control mechanism, to simultaneously control the variable working-angle control mechanism and the variable phase control mechanism responsively to a desired working angle and a desired phase both based on an engine operating condition, and the control unit executing a synchronous control that a time rate of change of the working angle and a time rate of change of the phase are synchronized with each other in a transient state that the engine operating condition changes.
According to another aspect of the invention, a variable intake-valve operating system for an engine enabling a working angle of an intake valve and a phase at a maximum lift point of the intake valve to be varied, comprises a first actuating means for continuously changing the working angle of the intake valve, a second actuating means for continuously changing the phase of the intake valve, a control unit being configured to be electronically connected to both the first and second actuating means, for simultaneously controlling the first and second actuating means responsively to a desired working angle and a desired phase both based on an engine operating condition, and the control unit executing a synchronous control that a time rate of change of the working angle and a time rate of change of the phase are synchronized with each other in a transient state that the engine operating condition changes.
According to a still further aspect of the invention, a method of controlling a variable intake-valve operating system for an engine enabling a working angle of an intake valve and a phase at a maximum lift point of the intake valve to be varied continuously, the method comprises initiating a working angle control, so that the working angle is brought closer to a desired working angle, initiating a phase control in parallel with the working angle control, so that the phase is brought closer to a desired phase, and executing a synchronous control between the working angle control and the phase control, so that a time rate of change of the working angle and a time rate of change of the phase are synchronized with each other in a transient state that an engine operating condition changes.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.